Abstract
Variations in the thermopower, electrical resistivity, magnetoresistance, thermal expansion coefficients, and their anisotropy with temperature were detected near room temperature in single crystals of weakly doped lanthanum manganites La1−xAxMnO3 (A = Ca, Sr; x = 0.07–0.125) with orthorhombic structure. The results obtained are discussed in terms of a model of phase separation related to polaron anisotropy. Due to a gain in exchange and elastic energies in the lattice, small-radius magnetic polarons can merge to form polarons of a larger size, which would contain now not one but rather a few electrons (equal in number to the polarons in the cluster). As a result, short-range order in a cluster and phase separation set in at a temperature Tps ≈ 250–300 K, which is approximately equal to the Curie temperature TC of conducting manganites with x ≈ 0.2–0.3.
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